Circuit architecture for mode switch

ABSTRACT

A current detection module capable of differentiating and quantifying contribution to a current signal generated by a sensor in response to stimulation by a certain target source from contributions from sources other than the target source (ambient sources) is disclosed. As long as the contribution from the target source comprises a pulsed signal, the module may synchronize itself to the pulse(s) so that there is a predetermined phase relationship between the pulse(s) and functions carried out by various stages of the module. The module may be re-used to also detect and quantify contributions from ambient sources by presenting these contributions to the module as pulses that trigger synchronization of the module. To that end, a detection system disclosed herein is based on the use of such current detection module and allows mode switching where, depending on the selected mode of operation, the module is configured to perform different measurements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority from U.S.Provisional Patent Application Ser. No. 62/029,361 filed 25 Jul. 2014entitled “Circuit Architecture for Mode Switch”, which is incorporatedherein by reference in its entirety.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure relates to the field of integrated circuits, inparticular to current detectors.

BACKGROUND

A photodiode (also referred to as “photodetector”) is a type of a sensorcapable of converting light into current or voltage. Generally, thephotodiode is a semiconductor device with a PIN or PN connectionstructure. When a photon of sufficient energy strikes the photodiode, itexcites electrons, creating free electrons and positively chargedelectron holes. The holes move toward the anode, and electrons towardthe cathode, and a photocurrent is produced proportional to the amountof incident light on the photodiode.

Other types of sensors include e.g. pyro-electric, piezo-electric, orcapacitive sensors.

All of these sensors are common in that they include a pair ofelectrodes and, when stimulated by their respective stimuli, the stateof charge across the electrodes changes. Current resulting from thechanged state of charge across the electrodes can then be used to detectand quantify the stimuli. For example, a photodiode produces a change inthe state of charge across its electrodes when the light is incident onthe photodiode. In other words, the photodiode generates current (whichmay be referred to as “photocurrent”) in the presence of light, wherethe current is proportional to the amount of light incident on thephotodiode. Similarly, a pyro-electric sensor produces a change in thestate of charge across its electrodes when heated or cooled, apiezo-electric sensor produces a change in the state of charge acrossits electrodes in response to the change in its mechanical orientation(e.g. strain), while a capacitive sensor is one where changes in theenvironment change the effective capacitance of the sense element, whichin turn changes the capacity to hold charge.

For such sensors, as well as other sensors operating according tosimilar principles of detecting change of charge state, it may bedesirable to be able to detect and quantify stimuli originating from aspecific source of interest as well as stimuli originating from allother sources besides the source of interest. For example, in context ofa photodiode, it may be desirable to detect and quantify a contributionto the current generated by the photodiode that is due to the detectionof light generated by a particular light source of interest, e.g. aparticular light emitting diode (LED), as well as to detect and quantifycontribution to the photocurrent that is due to the detection of lightgenerated by all other light sources besides this light source ofinterest.

Overview

Present disclosure relates to a current detection module capable ofdifferentiating and quantifying contribution to a current signalgenerated by a sensor as a result of stimulation by a certain source ofinterest (target source) from contributions from sources other than thesource of interest (ambient sources). As long as the contribution fromthe target source comprises a pulsed signal, the module synchronizesitself to the pulse(s) so that there is a predetermined phaserelationship between the pulse(s) and functions carried out by variousstages of the module. The module may be re-used to also provide highprecision detection and quantification of contributions to thesensor-generated current signal from ambient sources by presenting, tothe current detection module, the contributions from ambient sources asone or more pulses which, in turn, trigger synchronization of themodule. To that end, a detection system is provided that implements thecurrent detection module as described herein and allows mode switchingwhere, depending on the mode of operation being selected, the currentdetection module is configured to perform different kinds ofmeasurements.

Accordingly, in one aspect of the present disclosure, a detection systemincludes a sensor configured to generate a current signal, where thecurrent signal includes at least a first portion comprising acontribution to the current signal from a predefined source (i.e. asource of interest) and/or a second portion comprising a contribution tothe current signal from one or more sources other than the predefinedsource, such other sources referred to herein as “ambient sources.” Thedetection system further includes a current detection module configuredto receive the current signal generated by the sensor and generate adigital value indicative of the first portion of the current signaland/or a digital value indicative of the second portion of the currentsignal.

Furthermore, the detection system also includes a mode switch configuredto set the current detection module to operate in at least one of afirst mode, a second mode, and a third mode. In the first mode, thecurrent detection module is synchronized to the predefined source and isconfigured to generate the digital value indicative of the first portion(i.e. current detection module is configured to detect the contributionto the current signal from the source of interest, while cancelling,reducing, or rendering below the noise of the current detection modulethe contribution to the current signal from sources other than thesource of interest). In the second mode, the current detection module isconfigured to generate the digital value indicative of at least thesecond portion (i.e. the current detection module is configured to onlydetect the contribution to the current signal from the ambient sources)when the contribution to the current signal from the one or more sourcesother than the predefined source is in a first range of values. In thethird mode, the current detection module is configured to generate thedigital value indicative of at least the second portion (i.e. thecurrent detection module is configured to only detect the contributionto the current signal from the ambient sources) when the contribution tothe current signal from the one or more sources other than thepredefined source is in a second range of values, the second range ofvalues having an upper end higher than an upper end of the first rangeof values (i.e. ambient sources cause larger currents).

It should be noted that, in various embodiments, both the first andsecond portion need not always be present (e.g. the source of interestmay be off, or there may be no or negligible amount of contributionsfrom the ambient sources), and, if both present, not always do both needto be measured. Furthermore, in some embodiments of the second and thirdmodes, the current detection module may be configured to generate thedigital value indicative of not only the second portion but also thefirst portion (i.e. the current detection module is configured to detectthe contribution to the current signal both from the source of interestand ambient sources).

As will be appreciated by one skilled in the art, aspects of the presentdisclosure may be embodied in various manners—e.g. as a method, asystem, a computer program product, or a computer-readable storagemedium. Accordingly, aspects of the present disclosure may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Functions described in this disclosure may be implemented as analgorithm executed by one or more processing units, e.g. one or moremicroprocessors, of one or more computers. In various embodiments,different steps and portions of the steps of each of the methodsdescribed herein may be performed by different processing units.Furthermore, aspects of the present disclosure may take the form of acomputer program product embodied in one or more computer readablemedium(s), preferably non-transitory, having computer readable programcode embodied, e.g., stored, thereon. In various embodiments, such acomputer program may, for example, be downloaded (updated) to theexisting devices and systems (e.g. to the existing current detectionmodules or controllers of such modules, etc.) or be stored uponmanufacturing of these devices and systems.

Other features and advantages of the disclosure are apparent from thefollowing description, and from the claims.

BRIEF DESCRIPTION OF THE DRAWING

To provide a more complete understanding of the present disclosure andfeatures and advantages thereof, reference is made to the followingdescription, taken in conjunction with the accompanying figures, whereinlike reference numerals represent like parts, in which:

FIG. 1 is a simplified circuit diagram of a circuit architecture for acurrent detection module, according to some embodiments of thedisclosure;

FIG. 2 is a simplified diagram illustrating example details ofmeasurements associated with the circuit architecture, according to someembodiments of the disclosure;

FIG. 3 is a simplified diagram of other example details of measurementsassociated with the circuit architecture, according to some embodimentsof the disclosure;

FIG. 4 is a simplified diagram of yet other example details ofmeasurements associated with the circuit architecture, according to someembodiments of the disclosure;

FIG. 5 is a simplified diagram of an example detail of an applicationassociated with the circuit architecture, according to some embodimentsof the disclosure;

FIG. 6 is a simplified block diagram of another embodiment of thecircuit architecture;

FIG. 7 is a simplified block diagram of example details of anapplication of an embodiment of the circuit architecture, according tosome embodiments of the disclosure; and

FIG. 8 is a simplified circuit diagram of another embodiment of thecircuit architecture;

FIG. 9 is a simplified diagram of a detection system with modeswitching, according to some embodiments of the disclosure;

FIG. 10 is a simplified diagram of a sensor, according to someembodiments of the disclosure;

FIG. 11 is a simplified diagram of a mode switch, according to someembodiments of the disclosure;

FIG. 12 is a simplified diagram a mode switch, according to otherembodiments of the disclosure;

FIG. 13 is a simplified circuit diagram of a circuit architecture withmode switching, according to some embodiments of the disclosure;

FIG. 14 is a graph showing an LED pulse input to a mode switch overtime, according to some embodiments of the disclosure;

FIGS. 15A-15D show timing diagrams of four modes of operation of thedetection system with mode switching, according to some embodiments ofthe disclosure; and

FIG. 16 is a table summarizing four modes of operation of the detectionsystem with mode switching, according to some embodiments of thedisclosure.

DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE DISCLOSURE Exemplary CurrentDetection Module

Embodiments of the present disclosure are based on the use of a currentdetection module capable of differentiating and quantifying (i.e.measuring) the contribution to the current signal generated by a certainsource of interest from contributions from sources other than thepredefined source of interest, i.e. ambient sources. As long as thecontribution to the current signal from the predefined source comprisesa pulsed signal (referred to in the following as “pulse(s) ofinterest”), the current detection module is configured to synchronizeitself to the pulse(s) so that there is a predetermined phaserelationship between the pulse(s) and functions carried out by variousstages of the current detection module (referred to in the following asa “receiver circuit”). The pulsed signal of the source of interest mayinclude one pulse or multiple pulses, where a pulse may include one ormore frequency components. Ambient sources may also contain multiplefrequency components, possibly even the same components as those of thepulse of the predefined source of interest. Because the frequenciespresent in the pulse(s) of interest are synchronized to the receivercircuit (i.e. synchronized to the clock of the current detectionmodule), there is a certain known phase relationship between the currentdetection module and each of the frequency components of the pulse ofinterest (which phase relationship could be different for differentfrequencies in the pulse of interest, but nevertheless known ahead oftime). The current detection module is designed to detect pulsessynchronously and in a way that requires precise phase relationshipbetween the receiver circuit and the source of interest. While theambient sources may contain the same frequency components as the sourceof interest, the ambient sources are unlikely to contain precisely thesame amplitudes and phases that make up the pulses of interest (i.e.ambient sources are unlikely to be synchronized to the current detectionmodule). As a result, frequencies present in the ambient are averagedout even if the ambient sources contain very similar or the samefrequencies as the pulse of interest.

Much of prior art approaches where it is desired to detect and measurecontribution from a predefined source of interest from all otherpossible sources is based on avoiding interference with the ambientsource by choosing a frequency of the source of interest to be differentthan the frequencies present in the ambient. Inventors of the presentapplication realized that such approaches are not always successfulbecause the content of the ambient is often unpredictable. Inventors ofthe present application further realized that by synchronizing thereceiver circuit to the pulses of the signal of interest, it is possibleto detect and measure contributions from the source of interest inpresence of contributions from one or more ambient sources withouthaving to choose frequencies for the pulses of the signal of interestthat are different from the ambient (i.e. the frequency components couldbe the same).

An exemplary current detection module and functionality of such a moduleis now described in greater detail with reference to measurement ofphotocurrent signal generated by a photodiode in response to detectinglight from a light source (i.e. for the example that the currentdetection module is used to detect photocurrent). However, teachingsprovided herein are equally applicable to current detection modulesconfigured to detect currents generated by sensors, or chargegenerators, other than photodiodes, such as, but not limited to,pyro-electric, piezo-electric, or capacitive sensors. For all of thesesensors (i.e. some kind of charge generators), a general settingdescribed below for photodiodes is applicable where a sensor generates acurrent signal that may contain contributions from what may beconsidered as two “sources.” One “source” is a particular source ofinterest (i.e. the sensor sensing some event of interest—e.g. lightgenerated by a particular LED as detected by a photodiode, change intemperature due to a particular source of interest detected by apyro-electric sensor, mechanical deformation caused by a particularforce/source of interest as detected by a piezo-electric sensor, touchby e.g. a human or a stylus as detected by a capacitance sensor, etc.).The other “source” may be considered to include everything else besidesthe source of interest that may cause the change in the charge state ofthe sensor. Such a source is referred to as an “ambient source.” Inother words, the same sensor that senses contributions from the sourceof interest may also (or instead of, in case the source of interest isnot providing any contribution) sense other things—e.g. the photodiodemay detect ambient light, the capacitance sensor may sense touch that isnot by a human or a stylus, etc. One common goal for all of thesesensors may be to be able to distinguish and quantify these separatecontributions to the current generated by the sensors.

Referring now to the example of a photodiode as a sensor, someembodiments of the present disclosure provide for measurement ofphotocurrent signal from a light source, which may be synchronized(e.g., specifically modulated).

Common photodiode circuits (e.g., photodiode amplifiers) are typicallyconfigured for one of low noise, wide bandwidth, and high dynamic range.Such circuits do not generally provide all three characteristics (lownoise, wide bandwidth, and high dynamic range) simultaneously. Even ifsome circuits do provide all three characteristics, such circuits mayrequire high power, or may not provide for high signal extraction of atarget light source (especially in the presence of a high amount ofambient light, which is considered an interference and acts like noise),or may not be flexible to accommodate different sampling modes ormultiple channels.

For example, Burr Brown's OPT201 integrated photo-diode and amplifierprovides low noise operation, but does not have any means to distinguishbetween different types of light sources. In another example, New FocusInc.'s 1601 and 1611 high-speed photo-receivers have large gainbandwidth (GBW), low noise, high drive capability and large dynamicrange to enable wide bandwidth low-noise detection of signalsdistributed over fiber-optic cables, or found in applications such ashigh resolution spectroscopy, fiber-optic sensors, and opticalmetrology. The photo-receivers consist of a silicon or InGaAs PINphotodiode followed by a low-noise amplifier. However, thesephoto-receives are not capable of sampling multiple channels, and aredesigned such that there is no need to distinguish between differenttypes of light that fall on the sensor—predefined source of interest andthe ambient.

Turning to FIG. 1, FIG. 1 is a simplified block diagram of electricalcircuit 10 that may be used as a current detection module describedherein. Electrical circuit 10 is configured to simultaneously providelow-noise and low-power consumption (among other features) whileavoiding interference from uncorrelated sources besides the source ofinterest (for the example of a sensor being a photodiode, suchuncorrelated sources being e.g., sunlight, background light, ambientlight) in the environment. Furthermore, the circuit architecture isconfigured to have high dynamic range that is suitable for use in thepresence of a strong ambient source, such as e.g. sunlight, for theexample of a sensor being a photodiode. The circuit architecture can beextended to multiple channels, for example, in applications that involvereading multiple sensor (e.g. multiple photodiode) signals concurrently.

According to various embodiments, electrical circuit 10 can provide thefollowing features substantially simultaneously: low noise, high dynamicrange, high rejection of uncorrelated ambient sources, high signalextraction of a locked or target source (i.e. the source of interest),low power operation, and flexibility for different sampling modes.Furthermore, electrical circuit 10 can allow for simultaneous samplingof multiple channels for analog-to-digital conversion, improve ambientsignal rejection in the first mode, and measure ambient signal in thesecond mode. One example is ambient light rejection (ALR) in the firstmode when a sensor is a photodiode. Multiple channels are serviced by asingle and often more precise analog-to-digital converters (ADCs) whilemaintaining simultaneous measurement on all channels.

According to a specific embodiment, electrical circuit 10 may comprise asensor 12 that detects a stimuli from a target source of interest 14,e.g. a photodiode 12 that receives light from a light source 14. Thecurrent signal generated by the sensor 12 can include a single pulse oflow duty cycle or a multiple pulse train of low duty cycle (e.g.,depending on the duty cycle of target source 14). In some embodiments,the target source 14 may be modulated by an integrated circuit (notshown) coupled to electrical circuit 10.

According to various embodiments, electrical circuit 10 can comprisefour stages 16, 18, 20, and 22. Stage 16 can include a trans-impedanceamplifier (TIA), which may amplify the current signal from the sensor 12and generate a low noise signal. The trans-impedance amplifier can alsoconvert the current signal to a voltage at the output. Stage 16 includesa feedback capacitance 24 (CO in parallel with a feedback resistor 26(R_(f)) connected to an operational amplifier (op-amp) 28 in an R-Cfeedback loop, for example, to reduce noise and stabilize the circuit.

Any source of interest 14 (including DC source, e.g. DC light for theexample of a sensor being a photodiode) whose bandwidth is within theamplifier bandwidth may be amplified by amplifier 28. Generally,capacitance of a sensor can affect noise gain based on the relativevalue of the capacitance to resistance value R_(f) of feedback resistor26 and capacitance value C_(f) of feedback capacitor 24. Configuringstage 16 as a first stage can provide increased flexibility to minimizeexcess noise gain. In a general sense, two dominant noise sources inelectrical circuit 10 include Johnson noise of feedback resistor 26 andamplifier 28's input voltage noise. To reduce Johnson noise, resistancevalue R_(f) of feedback resistor 26 can be chosen to be as large aspossible consistent with the largest DC current that is expected for agiven arrangement of sensor 12 and other components. Such aconfiguration may provide minimum amplifier noise consistent with thetotal DC current. Capacitance value C_(f) of feedback capacitor 24 canbe chosen to change the bandwidth of the current signal (which may be ofthe order of approximately 1/τ, where τ refers to the input pulseduration) as desired. Stage 16 can also include a low pass filter (LPF)30 that additionally filters out high frequency noise in thephotocurrent signal. LPF 30 can also increase the duration of pulses ofthe current signal generated by sensor 12 (which may coincide with thepulse duration of the (synchronized) target source 14). The frequencythreshold of LPF 30 can be configured as desired based on particularneeds depending on the expected (or measured) noise characteristics.

Stage 18 may comprise a high pass filter, active or passive, withfrequency f_(ac), and a capacitor that provides AC coupling. Stage 18can eliminate low frequencies (e.g., remove DC) and allow high gain tobe provided in subsequent stages. The pulsed output from the stage 16 isfiltered by having low frequency components removed by stage 18, therebyproviding a zero cross-over point where the amplitude of the currentsignal changes from positive to negative. Stage 18 can eliminate some ofthe noise components from stage 16 and high frequency noise and lowerfrequency currents from ambient signal (e.g. ambient light) oruncorrelated ambient sources.

In some embodiments, a square pulse shaped signal from target source 14may be modified by the filtering action of LPF 30 and stage 18 toeliminate low frequencies. The corner frequencies (e.g., boundary in thefrequency response at which energy flowing through begins to reduce(attenuate or reflect)) of stages 16 and 18 may be chosen to maximizesignal measurement and provide ALR. For example, the corner frequency ofthe high pass filter of stage 18 can be set as large as 0.5/τ. Thechoice can also be influenced by the integration time chosen in nextstage 20.

Stage 20 may comprise integration and demodulation. A single polechangeover switch 34 may switch the incoming signal based on a clockfrom timer 36. The clock cycle of timer 36 may be configured to matchthe zero cross-over point of the photocurrent signal from stage 18. Whenthe zero cross-over point occurs, switch 34 may switch from integratingamplifier 38(1) to integrating amplifier 38(2). Two integratingamplifiers 38(1) and 38(2) may be used to integrate in succession on thepositive portion of the signal from stage 18 when switch 34 is connectedto the positive integrating amplifier 38(1) and on the negative portionof the signal from stage 18 when switch 34 is connected to the negativeintegrating amplifier 38(2). Each of positive integrating amplifier38(1) and negative integrating amplifier 38(2) may include a capacitorC_(int) configured to enable the operational amplifier therein tooperate as an integrator. In some embodiments, switches SW2 may be usedto reset positive integrating amplifier 38(1) and negative integratingamplifier 38(2), for example, after every conversion cycle or aftermultiple integration phases.

Each of positive integrating amplifier 38(1) and negative integratingamplifier 38(2) (generally referred to individually as an “integrator”38) acts like a storage element that produces an output voltage outputproportional to the integral of its input current (converted fromvoltage output of the previous stage) over time. In other words, themagnitude of the output voltage is determined by the length of time(integration period t_(int)) during which an input voltage is present asthe current through the feedback loop (comprising C_(int)) charges ordischarges capacitor C_(int). The circuit operates by passing a currentthat charges capacitor C_(int) over time from the input current of stage18. When the input current of stage 18 is firstly applied to theintegrator, the feedback capacitor C_(int) begins to charge and theoutput voltage is determined by the total charge (which is the integralof the input current over time).

Positive integrating amplifier 38(1) may generate a positive integratedvalue 40 (Q₊), which is the integral over time of the positive amplitudeof the alternating current signal from stage 18, and negativeintegrating amplifier 38(2) may generate a negative integrated value 42(Q⁻), which is the integral over time of the negative amplitude of thealternating current signal from stage 18. The integration period t_(int)can be configured over a wide range based on particular needs. The startof the integration cycle may be controlled by timer 36 in amicrocomputer, a simple programmable circuit, or other suitablecomponent. The gain of the amplifier can be chosen to optimizeconversion by an analog-to-digital convertor (ADC) 44 (as DC and lowfrequency components of ambient light are largely removed after stage18) at stage 22. At the end of the positive and negative integrationcycle, substantially all currents in the integration period t_(t) may beintegrated and the voltage may be held at the outputs of stage 20. Thevoltages may be subtracted either before conversion by a differenceamplifier or converted by ADC 44 and then subtracted digitally.

Mathematically, the integration and subtraction are similar to a lowpass filter and a “lock-in” filter to further remove noise artifacts ofthe ambient sources while amplifying the current signal. For example,the phase of switch 34 can be adjusted to provide “lock-in”functionality to a signal originating from a distant system. Assume,merely for illustrative purposes, and not as a limitation, that adistant light source produces a train of N pulses repeating at a rate R.Timer 36 can be configured to lock to the phase of the clock thatgenerates the N pulses. Thus a phase lock loop can be constructed tomeasure the light intensity of the distant light source. Positiveintegrating amplifier 38(1) and negative integrating amplifier 38(2) cantogether provide increased ALR. Outputs 40 and 42 may be fed to ADC (orADC integrated with a micro-controller) 44 at stage 22 to performfurther operations.

ADC 44 can read the output voltage of stage 20 and a controller thereincan reset integrators 38(1) and 38(2), for example, by momentarilyclosing SW2, to start a new integration cycle. The reset can occur atthe end of each pulse or at the end of a group of pulses. The voltage atstage 20 may represent a signal charge deposited at the sensor 12 as aresult of detecting stimuli from the target source 14 in addition tocharge from substantially all ambient interference. In an exampleembodiment, the pulses may be added together thereby increasing signalstrength and reducing noise and interference digitally after ADC 44. Inanother example embodiment, the pulses may be added in an analog domainuntil SW2 resets integrating capacitors C_(int). Embodiments ofelectrical circuit 10 can permit extension of the circuit architectureto ultra short pulses, for example in nanosecond and picosecond domain,without substantially increasing the speed of ADC 44. High dynamic rangemay be facilitated as digital additions of pulses can be carried outover many more pulses, almost without limit, than any analog addition onthe integrating capacitors C_(int) would permit.

According to various embodiments, i nput current generated by sensor 12may be converted to voltage at stage 16. Any frequency content of thevoltage signal may be shaped by the band pass filtering functions atstate 18. The output voltage of stage 18 may be converted back tocurrent, for example, using a suitable resistor, and integrated withcapacitor C_(int) over time t_(int) over positive and negative cycles.At least a portion of the behavior of electrical circuit 10 may beindicated by the following equations:

V_(TIA) = i_(p) × R_(f) V_(a c) = BPF(f_(filt)) × V_(TIA)$V_{int} = {\left( \frac{V_{a\; c}}{R_{i\; n}} \right) \times \left( {C_{int} \times t_{int}} \right)}$

where V_(TIA) is the output voltage at stage 16; i_(p) is the currentfrom sensor 12 (e.g. photovoltaic current for the example of sensor 12being a photodiode); R_(f) is the resistance of feedback resistor 26;V_(ac) is the output voltage at stage 18; BPF(f_(filt)) is a bandpassfilter shaping function of stage 18; V_(int) is the output voltage atstage 20; R_(in) is the resistance of a resistor (not shown) at stage20; C_(int) is the capacitance at stage 20; and t_(int) is theintegration time.

For example, Rf may be chosen to prevent saturation at stage 16 with ahigh amount of low frequency ambient sources, such as e.g. sunlight. Thecorner frequencies can be chosen to minimize interference whiletransmitting most of the signal pulse at stage 18. Moreover, the choiceof R_(in) and C_(int) can allow signal gain at stage 20 to match ADCinput range at stage 22. Further, multiple cycles of analog integrationover many pulses with digital integration at ADC 44 can allow a largedynamic range.

In some embodiments, an intense short pulse produced by target source 14may perform better for low power operation as the system of amplifiersand ADC can be powered down between the pulses. Also, for the same netpower consumed by synchronous target source 14, signal-to-noise-ratio(SNR) can be maximized by using the shortest possible pulse that can beproduced by a driver circuit. (The shortest possible pulse may belimited by the peak current output available.) Electrical circuit 10 maybe dynamically or programmatically configured in some embodiments, forexample, by changing the C_(f), R_(f), C_(int), and other passivecomponent values and corner frequency values as desired.

In some embodiments, the low frequency (e.g., DC) component of thecurrent signal generated by sensor 12 may be measured by directlyconnecting stage 16 to the input of ADC 44. Alternatively, the lowfrequency component may be measured by connecting stage 16 to eitherpositive integrating amplifier 38(1) or negative integrating amplifier38(2) of stage 20. In embodiments with low levels of ambient signals,one of positive and negative integrating amplifiers 38(1) and 38(2),respectively, may be connected directly to sensor 12, bypassing stages16 and 18.

According to various embodiments, at least some components of stages 16,18, and 20 are programmable (e.g., component values adjustable accordingto user specifications) after electrical circuit has been implemented ina physical form. The component values may be programmable manually, orby a suitable computing device or controller. For example, capacitanceC_(f) of feedback capacitor 24, resistance R_(f) of feedback resistor26; bandpass filter shaping function BPF(f_(filt)), resistance R_(in),capacitance C_(int) etc. can be programmed according to the applicationin which electrical circuit 10 is to be used. Thus, the same physicalrepresentation of electrical circuit 10 may have a first set ofcomponent values in one application (e.g., photoplethysmography (PPG)system used in controlled ambient light) and a different, second set ofcomponent values in a different application (e.g., wireless sensor usedin uncontrolled ambient light).

Turning to FIG. 2, FIG. 2 is a simplified diagram illustrating anexample signal chart 50 according to an embodiment of electrical circuit10. Merely for example purposes, and not as a limitation, the pulseduration τ was set at 1 μs, and the high pass filter corner frequency(of stage 18) was set at 300 kHz or 0.3/τ. The output of the stages wasreferred to the input to allow for easy comparison. Input photocurrentpulse 52 from synchronized light source may result in a photocurrentsignal 54, illustrated after stages 16 and 18. Signal 54 indicates an ACsignal, with a zero cross-over point. The zero cross-over point may setthe integrating cycle duration _(int). Positive and negative integrationcycles may be denoted by a line 56, which also has a zero cross-overpoint coinciding with the zero cross-over point of signal 54.

Turning to FIG. 3, FIG. 3 is a simplified diagram illustrating anexample signal chart 60 according to an embodiment of electrical circuit10. Input photocurrent pulse 62 from synchronized light source mayresult in a photocurrent signal 64, illustrated after stages 16 and 18.Signal 64 is an AC signal, with a zero cross-over point. The zerocross-over point may set the integrating cycle duration t_(int).Positive and negative integration cycles may be denoted by the line 66,which also has a zero cross-over point coinciding with the zerocross-over point of signal 64. Input photocurrent signal 62 may begenerated as pulses (e.g., with a short 1 μs pulse). Each pulse ofsignal 64 may be shaped by the action of stages 16 and 18. Positive andnegative integration cycles are applied to each pulse in the train ofpulses. The separation t_(s) between pulses may be configured based onthe settling time or to minimize any effect of particularly dominantfrequency components (if any) from ambient light.

Turning to FIG. 4, FIG. 4 is a simplified diagram illustrating a graph80 showing input charge over frequency of interfering ambient light.Graph 80 illustrates the suppression of ambient light according toelectrical circuit 10. Assume, merely for illustrative purposes, and notas a limitation, that a light source in the environment has a frequencyf. Further assume that the phase of the ambient light is somehowsynchronized to produce worst case interference at each possiblefrequency of the ambient light (indicated along the x-axis). Themeasured amplitude of the photocurrent signal produced at that frequencycan be reduced by the action of all four stages 16, 18, 20 and 22. Inthe case of a train of multiple pulses, suppression may be increasedeven further.

Graph 80 was generated using 16 pulses, and the input referredintegrated current (after stage 22) was calculated as charge on theY-axis. According to embodiments of electrical circuit 10, ALR of almosta factor of 100 at frequencies below 50 kHz may be observed. Manyambient light sources such as fluorescent lamps and light emitting diode(LED) lights have components at low frequencies. Very low frequenciessuch as 120 Hz may be suppressed by factors exceeding 1000 and DC lightmay be completely blocked.

It may be noted that embodiments of electrical circuit 10 may rejectelectrical noise injected at sensor 12 similar to rejection of currentsgenerated by ambient sources. Indeed, components of electrical circuit10 may not distinguish between currents generated by the sensor inresponse to stimuli of ambient sources or electromagnetic interference(EMI) or any other electrical noise injected into the circuit,facilitating robustness in the presence of both electrical interferenceand interference due to detection by the sensor of ambient source (e.g.optical interference for the example of sensor 12 being a photodiode).

Turning to FIG. 5, FIG. 5 is a simplified diagram illustrating anexample application 90 of electrical circuit 10 as used in aphotoplethysmography system 92. A photoplethysmograph is a device usedto optically measure changes in the effective light transmission orreflectance of an organ. Examples of photoplethysmography systemsinclude pulse oximeters, cardiovascular monitors, and respirationdetectors. Application 90 illustrated in the FIGURE can include a pulseoximeter, although electrical circuit 10 may be implemented in any othertype of photoplethysmography systems as well, within the broad scope ofthe embodiments.

The pulse oximeter of application 90 may include photodiode 12 andsynchronous light source (e.g., red and infrared light emitting LED)connected to photoplethysmography system 92, which can includeelectrical circuit 10 and other components, based on the particularapplication need. The pulse oximeter may be attached to, or otherwiseplaced in proximity with an organ (e.g., fingertip, wrist, etc.) 94(e.g., of the patient whose pulse is being monitored). Light emitted bysynchronous light source 14 may be partially reflected, transmitted,absorbed, and/or scattered by the organ (e.g., skin, surroundingtissues, and the blood at the fingertip) before it reaches photodiode12. The photocurrent signal from photodiode 12 can provide a measurementof the organ, for example, indicative of pulse rate, or oxygen content,etc.

Currently available pulse oximeters and other photoplethysmographysystems use caps, light proof enclosures, and other such devices toprevent ambient/background light from generating noise in thephotoplethysmography systems. With electrical circuit 10, such lightblocking enclosures (e.g., caps, boxes, etc.) need not be used, aselectrical circuit 10 includes noise reduction capabilities sufficientto overcome ambient and other background light noise. Moreover, becauseof the noise reduction characteristics of electrical circuit 10, and itsconsequent reduced sensitivity to ambient and DC light, the distancebetween synchronous light source 14 and photodiode 12 may be configuredbased on convenience factors, rather than noise reduction.

Turning to FIG. 6, FIG. 6 is a simplified block diagram illustratinganother embodiment of electrical circuit 10. Multiple (e.g., four)sensors 12, shown in FIG. 6 as photodiodes 12, may be connected to ADC44, for example, to measure light intensity from four different spatialorientations. In some embodiments, each sensor 12 may be connected toseparate stages 16, 18 and 20, with all sensors 12 sharing a common ADC44. Each of stages 20 may provide a positive integrated value and anegative integrated value to ADC 44. ADC 44 may sample the outputs froma specific stage 20 before proceeding to the next stage 20, and so on,until it samples the outputs from substantially all stage 20 within acertain time interval. The time interval may be configured according tothe power cycle of light source 14, such that ADC 44 completes samplingthe outputs from all stage 20 before light source 14 powers down.

Moreover, the output from stage 20 can remain constant after theintegration phase until reset, ADC 44 can be multiplexed to sample eachof the outputs without compromising performance. Thus embodiments ofelectrical circuit 10 can allow a relatively lower cost low speed ADCwith low frequency switching between channels can be used withoutcompromising performance. Such circuit architecture can be used inspecialized sensor applications, for example, that use lateralphotodiodes, quad detectors, or optical angle sensors in context of asensor being a photodiode. With the circuit architecture of embodimentsof electrical circuit 19, pulse width of the input light andsubstantially all components of stages 16, 18, and 20 can be configuredwith nanosecond pulses without substantially affecting ADC 44's samplerate.

Turning to FIG. 7, FIG. 7 is a simplified diagram illustrating anexample application 100 of electrical circuit 10. Smartphone 102 may beconfigured to detect gestures of a user 104 based on optical signals(rather than touch). Multiple photodiodes 12 may be configured onSmartphone 102 (e.g., on its display screen). Synchronous light source14 may be provided on Smartphone 102 in some embodiments. Light fromlight source 14 may be reflected off user 104, and may be measured byphotodiodes 12. The amount of light arriving at each photodiode 12 maydepend on the particular gesture (hand, finger or body position) of user104. When user 104 changes the gesture, the amount of light onphotodiodes 12 may also change. This change may be calculated by asuitably calibrated microcontroller to detect the gesture and derive asuitable meaning thereof. With electrical circuit 10 implemented in suchapplication 100, the sensitivity of the system to the background lightand other extraneous light may be reduced without compromising theperformance.

Turning to FIG. 8, FIG. 8 is a simplified circuit diagram illustratinganother example configuration of an embodiment of electrical circuit 10.Instead of ADC 44, a differential amplifier 110 may be used in stage 22.Differential amplifier 110 may compute a difference between outputs 40and 42 and send the difference to ADC 44 or other suitable component(e.g., microprocessor, digital signal processor, etc.). Differentialamplifier 110 may also amplify the difference in outputs 40 and 42, andthereby increase accuracy of measurement based on particular needs.

To summarize the above description, an example electrical circuit isprovided and includes a sensor (e.g. a photodiode) that receives asignal (e.g. light signal) from a target source (e.g. a target lightsource) and generates a current signal (e.g. a photocurrent signal), atrans-impedance amplifier that amplifies the current signal andgenerates a low noise signal, and a high pass filter that converts thelow noise signal into an AC signal having a positive amplitude, anegative amplitude, and a zero cross-over point between the positiveamplitude and the negative amplitude. The electrical circuit alsoincludes a positive integrating amplifier that receives the positiveamplitude of the AC signal and generates a positive integrated valueover an integration period, and a negative integrating amplifier thatreceives the negative amplitude of the AC signal and generates anegative integrated value over the integration period. The electricalcircuit further includes at least one ADC that receives the positive andnegative integrated values.

In a specific embodiment where the sensor is a photodiode, theelectrical circuit is coupled to a photoplethysmography system. Lightfrom the light source reflects off, or transmits through an organ beforereaching the photodiode, such that the photocurrent signal from thephotodiode can provide an indication of a measurement of the organ. Thephotoplethysmography system does not have to include a light blockingenclosure to keep out ambient light for accurate measurements.

A system is also provided that includes a plurality of sensors (e.g.photodiodes) that receive one or more signals from one or more targetsources (e.g. light sources), with each one of the sensors generating acurrent signal, a plurality of trans-impedance amplifiers, in which eachtrans-impedance amplifier amplifies the current signal from one of thesensors and generates a low noise signal, a plurality of high passfilters, in which each high pass filter converts the low noise signalfrom each trans-impedance amplifier into an AC signal having a positiveamplitude, a negative amplitude, and a zero cross-over point between thepositive amplitude and the negative amplitude and a plurality ofintegrators. Each integrator includes a positive integrating amplifierthat receives the positive amplitude of the AC signal from each highpass filter and generates a positive integrated value over anintegration period, and a negative integrating amplifier that receivesthe negative amplitude of the AC signal from each high pass filter andgenerates a negative integrated value over the integration period. Thesystem further includes an ADC that receives the positive and negativeintegrated values from the plurality of integrators.

Using Current Detection Module with Mode Switching

Embodiments of the present disclosure are further based on therecognition that a current detection module as described above may bere-used to not only detect and quantify contribution to the currentsignal from a predefined, target, source of interest, but also providehigh precision detection and quantification of contributions to thesensor-generated current signal from sources other than the predefinedsource. To that end, a detection system is provided that implements thecurrent detection module as described above and further allows modeswitching where, depending on the mode of operation being selected, thecurrent detection module is configured to perform different kinds ofmeasurements.

FIG. 9 is a simplified diagram of an architecture 112 for use ofdetection system 120 with mode switching, according to some embodimentsof the disclosure. As shown, detection system 120 may include sensor122, a mode switch 124, and a current detection module 126.

Current detection module 126 could be implemented as electrical circuit10 described above.

Sensor 122 could be implemented as sensor 12 described above, whichcould be e.g. a photodiode, a pyro-electric sensor, a piezo-electricsensor, or a capacitive sensor. In general, sensor 122 may be consideredto be a device comprising one or more charge collecting/generatingcapacitive elements, as shown in FIG. 10. As used herein, the term“capacitive elements” of a sensor refer to elements of a sensor capableof holding a certain charge or, in other words, possessing a certaincapacitance. Such capacitive elements may include capacitors built intothe sensor on purpose, shown in FIG. 10 with one or more designatedcapacitive elements 132, as well as capacitances that a sensor mayintrinsically possess without being included on purpose (i.e. “parasiticcapacitances” that may be built into the sensor itself and/or happen tobe in the circuit elements surrounding the sensor), such parasiticelements schematically illustrated in FIG. 10 as parasitic capacitiveelements 134.

Sensor 122 is configured to detect stimuli, shown in FIG. 9 with arrowsgoing to sensor 122, which could originate from one or more sources ofinterest, shown as “target source 128” in FIG. 9, and/or from one ormore sources which may comprise any sources that are not classified asthe target sources, shown as “ambient source 130” in FIG. 9. Targetsource 128 could be implemented as source 14 described above, whileambient source 130 could e.g. include various sources contributing toambient light (i.e. what is referred to as “ambient source 130” does nothave to be a single, definitive source, but could include any kind ofstimuli generator that a particular sensor 122 could detect).

Mode switch 124 is configured to control operation of current detectionmodule 126 in order to use the same current detection module 126 toperform different measurements in the following modes. In each of whatis referred to as a “first mode” and a “fourth mode” described herein,current detection module 126 is configured to detect contribution fromthe source of interest 128. The first and fourth modes differ in howexactly such contribution is detected. In each of what is referred to asa “second mode” and a “third mode” described herein, current detectionmodule 126 is configured to detect contribution from the ambient source130. The second and third modes differ in which ranges of signalintensity generated by ambient source 130 may be correctly measured. Inparticular, the second mode may be used to detect contributions fromambient sources is in a certain first range of amplitudes, while thethird mode may be used to detect contribution in a higher range ofamplitudes (which amplitudes could oversaturate sensor 122 resulting inincorrect measurement if measured in the second mode). In order tocontrol different modes of operation, mode switch 124 may be configuredto ensure that one or more of sensor 122, current detection module 126,and target source 128 are synchronized (which synchronization isdescribed in more detail below), as shown in FIG. 9 with dashed arrowsbetween mode switch 124 and each one of these elements.

In various embodiments, functionality provided by mode switch 124 may beimplemented different manners—e.g. in software, hardware, a combinationof software and hardware, etc.

FIG. 11 illustrates one example of implementing mode switch 124 insoftware. In such an embodiment, mode switch 124 may include at leastone processor 136 and at least one memory element 138, along with anyother suitable hardware and/or software to enable its intendedfunctionality. Mode switch 124 may be considered to include one or moremodules (not shown in FIG. 11) configured to carry out functionalitydescribed herein related to mode switching and synchronization, as wellas an interface (not shown in FIG. 11) to enable communication withother devices, e.g. sensor 122, current detection module 126, and targetsource 128 illustrated in FIG. 9. As a result of performingfunctionality described herein, mode switch 124 can ensure that currentdetection module 126 properly performs measurements in one of the modes.Optionally, in different embodiments, various repositories (not shown inFIG. 11) may be associated with mode switch 124, including, but notlimited to, e.g. a repository storing information related to targetsources 128, a repository storing information indicative ofspecifications and limitations of sensor 122, etc.

FIG. 12 illustrates one example of implementing mode switch 124 inhardware. In such implementation, mode switch 124 may be configured asan actual switch that could be in one of the following positions:position 142, where mode switch 124 connects the output of sensor 122 tothe input of the first stage (i.e., the TIA) of current detection module126 (i.e. as a result of sensor 122 receiving stimuli, current may flowfrom sensor 122 to current detection module 126); position 144, wheremode switch 124 connects the output of sensor 122 is not connected toanything (i.e., because the output of sensor 122 is open, current cannotflow from sensor 122 and, as a result of receiving stimuli, sensor 122accumulates charge, referred to as “floating” of sensor 122); orposition 146 where mode switch 124 connects the output of sensor 122 toa predefined reference voltage, e.g. to the common mode (CM) node of theTIA in the first stage of current detection module 126, or to some otherreference voltage (i.e. irrespective of how much stimuli sensor 122 isreceiving, sensor 122 is maintained to be at the reference voltage). Inan optional embodiment, mode switch 124 could be configured to connectsensor 122 to at least two different reference voltages, shown as afirst reference voltage V_ref1 in position 146 and a second referencevoltage V_ref2 in position 148. In various embodiments, mode switch 124may be implemented using any number of switches, connected in seriesor/and parallel, as suitable for a particular deployment of thedetection system 120. In various embodiments, one or more switches ofthe mode switch 124 may be implemented as complementarymetal-oxide-semiconductor (CMOS) switches.

Turning to FIG. 13, FIG. 13 is a simplified circuit diagram of a circuitarchitecture 150 with mode switching, according to some embodiments ofthe disclosure. Such an architecture can be used for one or more ofdetecting and measuring incoming signals from a target source at asensor and detecting, measuring, and cancelling incoming ambientsignals. FIG. 13 illustrates, and descriptions provided below refer to asensor being a photodiode. However, the same as for the descriptionsabove, these teachings are equally applicable to detections systemsemploying current detection module and mode switching as describedherein configured to detect currents generated by sensors, or chargegenerators, other than photodiodes, such as, but not limited to,pyro-electric, piezo-electric, or capacitive sensors.

According to a specific embodiment, circuit architecture 150 maycomprise a sensor 152 that detects a stimuli from a target source ofinterest 154, e.g. a photodiode 152 that receives light from a lightsource 154. Circuit architecture 150 may further include currentdetection module 160 comprising four stages (indicated in FIG. 13 asstages 162, 164, 166, and 168) similar to the four stages 16, 18, 20,and 22 of electrical circuit 10 described above. In addition, circuitarchitecture 150 may comprise a mode switch 170. Photodiode 152, LED154, mode switch 170, and current detection module 160 illustrated inFIG. 13 may be examples of, respectively, sensor 122, target source 128,mode switch 124, and current detection module 126 illustrated in FIG. 9.Therefore, all of the discussions provided for sensor 122, target source128, mode switch 124, and current detection module 126 are applicable tocorresponding elements shown in FIG. 13, which discussions, in theinterests of brevity, are not repeated here.

Comparison of FIGS. 1 and 13 reveals that FIG. 13 shows the four stagesof the circuit as illustrated in FIG. 1, except that sometimes elementsare denoted with different symbols. For example, the TIA 188 of FIG. 1(stage 1) is the same as the operational amplifier (op-amp) 28 in FIG.1, the bandpass filter (BPF) 190 of FIG. 13 (stage 2) is the same as ACelement 32 of FIG. 1, the +1/−1 integration switch 192 and integrator194 of FIG. 13 (stage 3) represent the same function as SW1 andintegrators 38(1) and 38(2) of FIG. 1. Similar to FIG. 1, in FIG. 13,positive and negative integrated values are provided to the ADC 198 ofstage 4, e.g. via a multiplexer 196 shown in configured to select onevalue at a time. Similar to FIG. 1, stage 1 of FIG. 13 is used to reducenoise and stabilize the circuit, stage 2 of FIG. 13 is used to remove DCfrom TIA bias as well as current generated by sensor 152 (e.g. toprovide first level immunity to low frequency ambient signals), stage 3of FIG. 13 is used for integrating both the positive and the negativetransient values (e.g. to provide second level immunity to ambientsignals), while stage 4 of FIG. 13 is used to digitize the integratoroutput.

Optionally, circuit architecture could include circuitry 180 for usingmeasurements of the circuit 160 in further digital signal processing,e.g. for gesture and/or proximity determinations. Optionally, circuitarchitecture may be configured to work with more than one target source,as shown with LED2 184. Further, photodiode 152 may be connected toswitch 200 for management of photodiode bias, which switch may beshorted during the times the photodiode is off.

In an embodiment, logic signals sent to the LED driver to pulse thetarget LED 154 (or any other target source) can be simply directed tothe switch 172 so that it pulses similar to the LED. This is shown as“PD switching” switch that directs LED pulse signals to the switch 172.

Mode switch 170 may be used to switch between measuring signals from thetarget source 154 and measuring integrated ambient charge. In oneembodiment, as shown in FIG. 13, mode switch 170 may be implemented byincluding two switches, switches 172 and 174, connected in parallel. Invarious implementations, mode switch 170 may be used to e.g. measure LEDlight synchronized to the LED pulse generator circuits or it may be usedto measure ambient light. Depending on the timing and connection of themode switch 170, four different tasks can be carried out by the samecircuit architecture, as described in further detail below.

In a first mode (normal mode), mode switch 170 is used as a bypass toconnect the output of sensor 152 to TIA 188 of the first stage of thecurrent detection module 160 and is primarily used to measure theresponse to an LED pulse, in the same manner as described above withreference to electrical circuit 10 (therefore, all of the discussionsprovided above for circuit 10 are applicable here). The response of therest of the circuit is illustrated in FIG. 14. In this mode, the goal isto measure light falling on the detector that only corresponds to theillumination by a certain target LED and reject ambient light (whichcould include sunlight, light from other LEDs or from any other lightsources). As was described with reference to electrical circuit 10 andillustrated in FIG. 14, this is accomplished in four stages: (1) amplifythe photocurrent and convert it to voltage (TIA stage), (2) pass theoutput of stage 1 through the BPF 190 to remove the DC portion of thephotocurrent which predominantly consists of the ambient light since theLED pulse is relatively short in time duration (see LED pulses andoutput of BPF in FIG. 14), (3) integrate the AC output of stage 2 withthe integrator 192-194 that switches sign at the zero crossing (seeintegration pulses in FIGS. 14), and 4) digitize the integrator outputusing ADC 198, with an optional MUX 196 to allow multiple channels toshare a single ADC.

As mentioned above, in the first mode, current detection module 160 canprovide two levels of protection from ambient light. First, low DC lightis reduced or blocked in stage 2. Then, positive and negativeintegrations by the integrator of stage 3 further reduce or block anyremaining ambient light. Thus, the architecture 150 allows cancellingambient signals without contributing additional computational load tothe circuit. As used herein, in this context, the term “cancelling”refers to cancelling ambient signals, reducing ambient signals, orrendering ambient signals below the noise of the current detectionmodule.

Thus, the mode switch 170 is used as a bypass and the rest of thecircuit architecture cancels ambient light. In one example, pulsed LEDlight falls on the mode switch 170. FIG. 14 shows a graph of an LEDpulse input to a mode switch 170 over time, according to someembodiments of the disclosure. The blinking LED light results in sensor152 generating current pulses as shown in FIG. 14 with ““LED pulses”. Asshown in the circuit architecture 150, the square electrical pulsesgenerated by sensor 152 in response to the light generated by LED 154are input into the TIA 188, and the pulses may be band pass filtered instage 1 (e.g. with the low-pass filter 30 as shown in FIG. 1). Thepulses are then passed through an AC filter to remove the DC (i.e.through the BPF 190 of stage 2), where the output of this stage is shownin FIG. 14 with “O/P BPF.” An integrator is used to recover the charge,which is represented by the area under the curve O/P BPF, and to cancelany DC that passed through the BPF 190. The integrator uses positiveintegration in a first (positive) phase of the cycle, and negativeintegration in the second (negative) phase of the cycle in order to addboth parts of the cycle and capture the charge. In the first mode, theoperations in the four stages of the current detection module asdescribed herein result in an excellent rejection of the ambient lightwhile only measuring the total number of photons reaching the detectorfrom the LED pulse of the target LED. In order to enable such operation,various parts of the architecture 150 need to be synchronized, where,besides being provided by the design choices made in implementingvarious elements of the architecture 150, the synchronization may becontrolled/managed by mode switch 170. Synchronization is also importantfor other modes of operation of the current detection module describedherein. Such synchronization is described below with reference to FIGS.15A-15D.

FIGS. 15A-15D show timing diagrams of four modes of operation of thedetection system with mode switching, according to some embodiments ofthe disclosure. Each of FIGS. 15A-15D illustrate five rows that show thesynchronization in time between various elements. The first row in eachof the FIGS. 15A-15D illustrates state of the mode switch 170. Thesecond row in each of the FIGS. 15A-15D illustrates stimuli (signal)generated by the source of interest (e.g. LED pulses generated by thetarget LED). The third row in each of the FIGS. 15A-15D illustratesinput signal provided to the first stage (TIA 188) of the currentdetection module. The fourth row in each of the FIGS. 15A-15Dillustrates output of the second stage (BPF 190) of the currentdetection module. The fifth row in each of the FIGS. 15A-15D illustratesswitching of the integration sign by the switch 192 in stage 3 of thecurrent detection module. The timing diagrams of FIGS. 15A-15D representthe relative sequence of events in the signal chain of receiving andprocessing signals. Synchronization between the elements of thedetection system described herein refers to the fact that these eventshave specific and well defined relationship in each of the measurementmodes.

The timing diagram for the first mode is illustrated in FIG. 15A. In thefirst mode, the arrival of light from the LED 154 (or a stimulusgenerated by any other target source) at the photodiode 152 (or anyother appropriate sensor), sets off a sequence of events. In otherwords, arrival of signal pulses generated by the target source at thesensor controls the timing of operations performed by the currentdetection module. First row of FIG. 15A illustrates that, in the firstmode, the mode switch 170 is closed (i.e. the output of the photodiode152 is connected to the first stage input of the current detectionmodule 160). LED pulses generated by the LED 154 (shown in the secondrow of FIG. 15A) are detected by the photodiode 152 and the photodiode152 generates current that flows to the TIA 188 (shown in the third rowof FIG. 15A). There normally is a certain time delay between the LEDpulses shown in the second row and TIA pulses shown in the third row ofFIG. 15A (and other FIG. 15), as a person of ordinary skill in the artwould immediately recognize, but since this delay is common and does notrelate to the synchronization of the elements of the detection systemdescribed herein, it is not illustrates in FIG. 15A (and other FIG. 15).

Values of the stimulus generated by the target source (e.g. width of theLED pulse) as well as various circuit elements of the current detectionmodule, such as e.g. bandwidth of the TIA 188, corner frequencies of theBPF 190, etc., define the time delay (shown in FIG. 15A as “t_(delay)”)from the beginning of the LED pulse to the time the zero crossing occursin the output of the BPF 190. In other words, the location of the zerocrossing depends on the value settings for the target stimulus and thevalues of the circuit elements of the current detection module 160. Allof these values are fixed by the circuit or the user (e.g. the userprovides the settings for the target stimulus) and thus the zerocrossing occurs at a specific time t_(delay) from the application of thestimulus. The integration sign should be changed at the time the zerocrossing occurs. Since it is possible for the detection system todetermine when the zero crossing occurs for a particular target sourceof interest, the system may be configured to set the timing of theintegration switch 192 to switch from +1 to −1 integration in dependence(i.e. with respect to) the stimulus so that the transition of the switch192 from +1 to −1 coincides with the zero crossing. This is illustratedin FIG. 15A where the integration sign shown in the fifth row changes atthe same time as zero crossing in BPF output occurs. It is this specificrelationship that allows the current pulse from the input to the TIA 188to be integrated in such a way that both the positive and the negativeoutput from the BPF filter 190 contribute to the measured signal, i.e.they are added. Any ambient light, irrespective of its frequency orshape, is quite unlikely to coincide precisely to this internallygenerated integration switch and thus, on an average, is cancelledduring the positive and negative integration phases. When many of thesepulses are added, due to such synchronization between the target sourceand the current detection system, current pulses resulting from thetarget source will continue to add to the previous values. On the otherhand, at the output of the integration of stage 3, current values fromthe ambient sources will have values that are sometimes positive andsometimes negative (because the integration sign is not switchedsynchronously with the ambient sources), and thus will be averagedtowards zero. Thus, the current detection module 160 allowssynchronizing the sign change of the integration of stage 3 to thepulsed signal of interest, so that the integrator output is added forthe pulsed signal of interest but the ambient signals are, on average,cancelled out due to lack of their synchronization with the sign change.

It should be noted that the timing diagram for the first modeillustrated in FIG. 15A is comparable to the timing diagram illustratedin FIG. 3, except that FIG. 3 illustrates various metrics in the samegraph (as opposed to rows of FIG. 15A) and illustrates an input currentgenerated by the sensor (“input photocurrent pulse”) instead of a pulsegenerated by the target source (“LED pulse”).

In a second mode (which could be referred to as a “floating” sensormode), one goal is to measure the ambient contributions only. In such acase, there is no natural pulsing of ambient sources, as was the casewith the pulsed target source 154, (because, unlike target sources thatmay be controlled, ambient sources are typically not controlled).However, in this mode, the mode switch 170 may be operated in such a waythat the sensor 152 itself can be used as the integrator, artificiallygenerating what looks, to the current detection module 160, as a currentpulse similar to that generated in the first mode when LED pulse isdetected. To that end, capacitance associated with the sensor 152 (e.g.the designated capacitive elements as well as parasitic capacitiveelements as shown in FIG. 10) can be used to integrate the chargegenerated by the sensor as a result of receiving stimuli from ambientsources.

The cycle of the second mode may begin by the mode switch 170 ensuringthat the output of sensor 122 is not connected to anything (this may beachieved e.g. by having mode switch in position 144 illustrated in FIG.12 and may be considered as the mode switch 170 being open). This isshown in the first row of FIG. 15B providing the timing diagram for thesecond mode.

At the time the mode switch 170 is open, signals generated by one ormore ambient sources are detected by the sensor 152, resulting in thesensor 152 generating charge on the capacitors of the sensor. Targetsources 154 may be off (i.e. not generating signals that are detected bythe sensor 152), as shown in the second row of FIG. 15B (no LED pulse).Because the output of the sensor 152 is not connected to anything,current cannot flow, so the charge accumulates/integrates on thecapacitive elements of the sensor 152. This continues for a certain timeperiod (which could be referred to as “integration time” or “floatingtime”), which could e.g. be user-defined or could be dynamicallydetermined by the detection system based on the maximum charge that canbe stored.

After this certain time period, the mode switch 170 connects the outputof sensor 152 to the current detection module 160, as shown in the firstrow of FIG. 15B with the mode switch being “closed.” As a result ofmaking this connection, the charge stored on the capacitive elements ofthe sensor 152 will discharge through the current detection module (e.g.through the TIA 188) and make a pulse of current, shown in the third rowof FIG. 15B. As far as the rest of the current detection module 160 isconcerned, this pulse of current looks just like a pulse received fromthe sensor 152 in the first mode as a result of sensor 152 detecting apulse generated by the target source. In other words, operation when, inthe second mode, the mode switch 170 first makes sure that the output ofsensor 152 is not connected to anything and accumulates charge and thenconnects the output of sensor 152 to the current detection module 160,artificially generates a current pulse that is provided to the TIA 188.The rest of the architecture of the current detection module 160 maythen be used in a manner analogous to how a current pulse was processedin the first mode because, as described above for the first mode, it isthe receipt of this current pulse by the current detection module thatdefines the timing of other operations and elements of the currentdetection module. For example, as described above, occurrence ofzero-crossing (shown in the fourth row of FIG. 15B) happens after apredefined time period after the receipt of the TIA pulse, and thecurrent detection module 160 is configured to switch the integrator signof stage 3 at the time when the zero-crossing takes place (shown in thefifth row of FIG. 15B).

Thus, in the second mode of operation of the current detection module160, providing an artificially generated current pulse to the currentdetection module 160 (by means of the mode switch 170) allows benefitingfrom the synchronization between the elements provided by the module toaccurately measure the pulse. In this mode, because the pulse isgenerated as a result of the sensor 152 detecting contributions from theambient sources only (target sources were off), the value generated bythe current detection module is representative of contributions to thesensorgenerated current signal due to the ambient sources. In otherwords, a current pulse artificially generated in the second mode, whenintegrated, directly represents the total accumulated charge and hencethe strength of the ambient.

In some embodiments of the second mode, stage 2 (i.e. BPF 190) of thecurrent detection module 160 may be removed/bypassed because in thismode it is not necessary to eliminate low frequency/DC contributionstypical of ambient light in the first mode. Thus, the current pulseshaped by the TIA 188 may be integrated directly, without passingthrough the BPF stage. In such embodiments, the timing of theintegration switch may be adjusted to include the entire integration ofthe pulse in the positive or the negative cycle. When the second stageis bypasses, zero-crossing point is defined in the output of the TIA188.

The switching integrator stage (stage 3) is maintained in the secondmode. The positive-negative cycle removes many integrator offsets. Ifthe integration time on the sensor (i.e. the time the sensor 152 isfloating) is τ and contributions from the ambient sources result insensor 152 generating current i_(amb), the total charge Q=i_(amb)τ canbe measured by the detection system as described herein with high SNR bysimply increasing the floating time until the charge accumulated on thesensor 152 is greater than the measurement noise floor.

In some implementations, internal leakage currents may limit thefloating time. For example, for a relatively large photodiode of 100 μmin size, one lux of light will make for roughly 4-5 pA of current,which, when integrated for 1 ms, results in 8 fC of accumulated chargethat can be measured.

As the foregoing illustrates, the same current detection module can beused to either measure contributions from the ambient sources orcontributions from synchronous pulse(s) generated by a target source.

In an embodiment, mode switching functionality used to create a pulse inthe ambient input as described for the second mode may be implementedwith the mode switch 170 comprising the switches 172 and 174. In such anembodiment, the first switch 172 may be connected to the second switch174. When the second switch 174 is open, the charge from the sensor 152has nowhere to go and the mode switch 170 integrates the accumulatedcharge on the sensor. Then the second switch 174 is closed to the TIA188, and the charge is transmitted through to the TIA 188 like a pulseof target source in the first mode. In this manner, ambient signals arecaptured and turned into pulsed signals. The pulses are then processedby the rest of the circuit in the same manner as the target sourcepulses were processed in the first mode.

A third operating mode may also be used to measure ambient contributionsonly, but this mode may be used particularly advantageously in apresence of fairly strong contributions from ambient sources (e.g. inpresence of strong ambient light). In such situations, it may beundesirable to integrate the charge on the sensor 152 as was done in thesecond mode because, when ambient contributions are strong, suchintegration is likely to lead to saturation of the sensor 152 (i.e.reaching the maximum amount of charge that the capacitive elements ofthe sensor 152 are able to hold) in a very short amount of time. Asaturated sensor cannot produce accurate measurements because it isclipped at the maximum values. This mode of operation may also beadvantageously used with certain types of sensors that may functionbetter when the voltage remains constant during the measurement, e.g.pyro sensors biased at a constant voltage and photodiodes for measuringintense light. In all these situations, it may be desirable to measurethe current generated by the sensor 152 directly, without integratingthe charge on the sensor as was done in the second mode. In suchsituations, the mode switch 170 can be used, again, to effectivelygenerate what looks like a current pulse that can be processed by thecurrent detection module 160. Thus, similar to the second mode, in thethird mode, there is no natural pulsing of ambient sources but the modeswitch 170 may be operated to artificially generate what looks, to thecurrent detection module 160, as a current pulse similar to thatgenerated in the first mode when LED pulse is detected. The rest of thearchitecture of the current detection module 160 may then be used in amanner analogous to how a current pulse was processed in the first modebecause it is the receipt of this current pulse by the current detectionmodule that defines the timing of other operations and elements of thecurrent detection module (i.e., as in the second mode, it is possible tobenefit from the synchronization between the elements provided by themodule to accurately measure the pulse).

In the third mode, at certain times (shown in FIG. 15C as “t_(Vref)”)the mode switch 170 connects the output of the sensor 152 to a certainreference voltage (e.g. common mode voltage of the TIA 188, V_cm) nodeso that no current passes through the TIA 188 (i.e. as far as the TIA188 is concerned, the mode switch 170 is open, as illustrated in thefirst row of FIG. 15C). At this time, target sources 154 may be off(i.e. not generating signals that are detected by the sensor 152), asshown in the second row of FIG. 15C (no LED pulse), and only signalsgenerated by one or more ambient sources are detected by the sensor 152.Because the sensor 152 is connected to the reference voltage and notconnected to the current detection module 160, there is no current goingto the TIA 188 during the times t_(vref) (as shown in FIG. 15C in thethird row).

At certain other times (shown in FIG. 15C as “t_(pulse)”), the modeswitch 170 connects the output of the sensor 152 to the input of theamplifier 188. When this happens, current (representative of the ambientsource contributions) can flow from the sensor 152 to the TIA 188,resulting in the TIA 188 receiving a current pulse similar to thecurrent pulse made, in the first mode, by the target source. Themagnitude of the current pulse can be measured in the same way asdescribed above.

Thus, in the third mode, the mode switch 170 is configured toeffectively generate what looks like a current pulse from a constantstimulus arriving at the sensor 152. This is done by pulsing the modeswitch 170 to connect for a specific amount of time to the amplifier'sinput (t_(pulse)) and otherwise the sensor 152 remains connected to afixed reference voltage, e.g. to the common mode voltage of theamplifier through the switch 174 shown in FIG. 13). With suchimplementation, the sensor always has the same potential on itsterminals and the TIA 188 does not receive current generated by thesensor 152 except for the times when that current is momentarilydirected into the TIA 188, resulting in one or more current pulses onthe TIA 188 as shown in the third row of FIG. 15C. Such current pulsesis similar to the current pulse of from the target source of the firstmode and the rest of the operation of the current detection module 160proceeds as described above for the first and second modes, whichdescriptions, in the interests of brevity, are not repeated here. Fourthand fifth rows of FIG. 15C illustrate synchronization as describedabove.

In one embodiment, the third mode described herein could be modified bymeasuring sensor node between two different reference voltages, therebymeasuring the changes to the sensor itself as the voltage is pulsed.This embodiment may be implemented in the same manner as the third modedescribed above, except that, at times shown in FIG. 15C as t_(Vref),the mode switch 170 connects the output of the sensor 152 to a certainreference voltage that is different from the common mode voltage V_cm.For example, if switch 174 were connected to V_ref and the switch 172were pulsed, and if V_ref were to be different than V_cm, then thepotential on the sensor is changed as switch 172 is pulsed. Thus thecurrent flowing into the amplifier depends not only on the ambientcurrent but also on the differences in the charge due to differentpotentials—V_cm when connected to the input of the amp and V_refotherwise. This will provide input pulse to the amplifier even in theabsence of any ambient. This flow of current originates purely from thechanges in potential is directly proportional to the capacitance of thenetwork. Simply, the net charge flowing into the amplifier during“pulse” is ΔQ=C ΔV where the difference between the two potentials isΔV. As previously described herein, this capacitance (be it capacitanceitself, or state of the sensor such as pyro, PZT, inductive etc.) can bechanged by the environment and measured. Thus this modification of thethird mode allows direct measurement of the “state of the sensor” andhence it's environment.

A fourth operating mode, illustrated in the timing diagram of FIG. 15D,may be considered as a combination of the first and second modesdescribed above in that both pulsing of the target source 154 andfloating of the sensor 152 are used. In this case, the sensor 152 isfloating for a certain time period (shown in FIG. 15D as “t_(f1)”) whenthe target source is off (in the second row of FIG. 15D, LED pulse isshown to be off during time t_(f1)), followed by the output of thesensor 152 being connected to the input of the TIA 188 for a certaintime period (shown in FIG. 15D as “t_(pulse1)”), resulting in a currentpulse as described above for the second mode (shown in the third row ofFIG. 15D as current pulse “ambient”). Because the target source 154 wasoff in the time when the sensor was floating, this current pulse, whenintegrated (see first integration in the fifth row of FIG. 15D),directly represents the total accumulated charge and hence the strengthof only the ambient.

After that, the sensor 152 is floating again for a certain time period(shown in FIG. 15D as “t_(f2)”, which time period may but does not haveto be equal to t_(f1)), except that now the target source is on (in thesecond row of FIG. 15D, LED pulse is shown to be on during time t_(f1)).Since the sensor 152 is floating (i.e. no current is flowing to the TIA188) when the target source is on, during this time t_(f2), the chargeaccumulated on the capacitive elements of the sensor 152 is due to bothcontributions of the ambient and the target source. Again, as in thesecond mode above, the output of the sensor 152 is then connected to theinput of the TIA 188 for a certain time period (shown in FIG. 15D as“t_(pulse2)”), resulting in a current pulse as described above for thesecond mode (shown in the third row of FIG. 15D as current pulse“ambient+target”), except that now, because the target source 154 was onin the time when the sensor was floating, this current pulse, whenintegrated (see the second integration in the fifth row of FIG. 15D),directly represents the combined strength of ambient and target sources.By subtracting the value generated by the current detection module 160indicative of measurements of the first pulse (ambient) from the valueindicative of measurements of the second pulse (ambient+target), a valueindicative of the contribution of the target source only is obtained.

In some embodiments of the fourth mode, the mode switch 170 may bedisconnect the output of the sensor 152 from the TIA 188 immediatelyfollowing the discharge of the sensor 152 in the first current pulse, asshown in FIG. 15D. However, in other embodiments, this may be done sometime later, as long as the timing is such that the target source isturned on when that disconnection occurs (i.e. when the sensor 152starts floating again).

Considerations provided above for the second mode are applicable, exceptfor the differences in that target source is sometimes on, to the fourthmode, and, therefore, are not repeated here. In particular, in thefourth mode (as well as in the third mode), in some embodiments, thesecond stage (BPF) of the current detection module 160 may be bypassedand the output of the TIA 188 may be presented directly to theintegrator stage.

The fourth mode may be particularly advantageous for situations whereambient light is weak or has low modulation frequency compared to pulsewidth, in which cases the fourth mode can provide enhanced SNR whencompared to multiple pulses in the first mode.

The four modes described above are summarized in the table in FIG. 16for the example of sensor 152 being a photodiode.

For the example of sensor 152 being a photodiode, according to variousimplementations, the LED light can be any color. For example, a red or agreen LED light may be used. Similarly, the LED pulse width can be anyselected width, and in one example, the LED pulse width is about 3 μs.In other examples, the LED pulse width is less than about 3 μs, or morethan about 3 μs. Pulse width of few ns to 100's of microsecond is atypical range for LED pulsewidths. The measurements can be repeatedfirst as a burst of pulses, which are themselves repeated at variousrates ranging from 0.01 Hz to many kHz.

In other embodiments when sensor 152 is a photodiode, the target lightsource could be any controllable light source, not necessarily a LED.Thus, target light sources could be, but are not limited to, e.g. laserdiodes, high/low pressure gas discharge sources, inorganic/organic lightemitting diodes, incandescent sources, halogen sources, etc.

Variations and Implementations

Note that in this Specification, references to various features (e.g.,elements, structures, modules, components, steps, operations,characteristics, etc.) included in “one embodiment”, “exampleembodiment”, “an embodiment”, “another embodiment”, “some embodiments”,“various embodiments”, “other embodiments”, “alternative embodiment”,and the like are intended to mean that any such features are included inone or more embodiments of the present disclosure, but may or may notnecessarily be combined in the same embodiments.

In one example embodiment, parts or entire electrical circuits of theFIGURES may be implemented on a motherboard of an associated electronicdevice. The motherboard can be a general circuit board that can holdvarious components of the internal electronic system of the electronicdevice and, further, provide connectors for other peripherals. Morespecifically, the motherboard can provide the electrical connections bywhich the other components of the system can communicate electrically.Any suitable processors (inclusive of digital signal processors,microprocessors, supporting chipsets, etc.), memory elements, etc. canbe suitably coupled to the motherboard based on particular configurationneeds, processing demands, computer designs, etc. Other components suchas external storage, additional sensors, controllers for audio/videodisplay, and peripheral devices may be attached to the motherboard asplug-in cards, via cables, or integrated into the motherboard itself.

In another example embodiment, parts or entire electrical circuits ofthe FIGURES may be implemented as standalone modules (e.g., a devicewith associated components and circuitry configured to perform aspecific application or function) or implemented as plug-in modules intoapplication specific hardware of electronic devices. Note thatparticular embodiments of the present disclosure may be readily includedin a system on chip (SOC) package, either in part, or in whole. An SOCrepresents an IC that integrates components of a computer or otherelectronic system into a single chip. It may contain digital, analog,mixed-signal, and often radio frequency functions: all of which may beprovided on a single chip substrate. Other embodiments may include amulti-chip-module (MCM), with a plurality of separate ICs located withina single electronic package and configured to interact closely with eachother through the electronic package. In various other embodiments, theamplification functionalities may be implemented in one or more siliconcores in Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs), and other semiconductor chips.

It is also imperative to note that all of the specifications,dimensions, and relationships outlined herein (e.g., the number ofprocessors and memory elements, logic operations, etc.) have only beenoffered for purposes of example and teaching only. Such information maybe varied considerably without departing from the spirit of the presentdisclosure, or the scope of the appended claims. The specificationsapply only to one non-limiting example and, accordingly, they should beconstrued as such. In the foregoing description, example embodimentshave been described with reference to particular processor and/orcomponent arrangements. Various modifications and changes may be made tosuch embodiments without departing from the scope of the appendedclaims. The description and drawings are, accordingly, to be regarded inan illustrative rather than in a restrictive sense.

Note that with the numerous examples provided herein, interaction may bedescribed in terms of two, three, four, or more electrical components.However, this has been done for purposes of clarity and example only. Itshould be appreciated that the system can be consolidated in anysuitable manner. Along similar design alternatives, any of theillustrated components, modules, and elements of the FIGURES may becombined in various possible configurations, all of which are clearlywithin the broad scope of this Specification. In certain cases, it maybe easier to describe one or more of the functionalities of a given setof flows by only referencing a limited number of electrical elements. Itshould be appreciated that parts or entire electrical circuits of theFIGURES and its teachings are readily scalable and can accommodate alarge number of components, as well as more complicated/sophisticatedarrangements and configurations. Accordingly, the examples providedshould not limit the scope or inhibit the broad teachings of parts orentire electrical circuits as potentially applied to a myriad of otherarchitectures.

Numerous other changes, substitutions, variations, alterations, andmodifications may be ascertained to one skilled in the art and it isintended that the present disclosure encompass all such changes,substitutions, variations, alterations, and modifications as fallingwithin the scope of the appended claims.

Although the claims are presented in single dependency format in thestyle used before the USPTO, it should be understood that any claim candepend on and be combined with any preceding claim of the same typeunless that is clearly technically infeasible.

What is claimed is:
 1. A detection system comprising: a sensorconfigured to generate a current signal, the current signal comprisingat least a first portion comprising a contribution from a target sourceand/or a second portion comprising a contribution from one or moresources other than the target source; a current detection moduleconfigured to receive the current signal generated by the sensor andgenerate a digital value indicative of the first portion of the currentsignal and/or a digital value indicative of the second portion of thecurrent signal; and a mode switch configured to set the currentdetection module to operate in one of a first mode, a second mode, and athird mode, wherein: in the first mode, the current detection module isconfigured to generate the digital value indicative of the firstportion, in the second mode, the current detection module is configuredto generate the digital value indicative of at least the second portionwhen the contribution from the one or more sources other than the targetsource is in a first range of values, and in the third mode, the currentdetection module is configured to generate the digital value indicativeof at least the second portion when the contribution from the one ormore sources other than the target source is in a second range ofvalues, the second range of values having an upper end higher than anupper end of the first range of values.
 2. The detection systemaccording to claim 1, wherein the mode switch and the target source aresynchronized so that the mode switch is configured to set the currentdetection module to operate in the first mode when the target source isgenerating the contribution to the current signal, and configured to setthe current detection module to operate in the second mode or in thethird mode when the target source is not generating the contribution tothe current signal.
 3. The detection system according to claim 1,wherein the mode switch is further configured to set the currentdetection module to operate in a fourth mode, wherein in the fourthmode, the mode switch is configured to: set the current detection moduleto operate in the second mode for a first period of time while thetarget source is not generating the contribution to the current signalto generate a first digital value indicative of the second portion inabsence of the first portion, and set the current detection module tooperate in the second mode for a second period of time while the targetsource is generating the contribution to the current signal to generatea second digital value indicative of a total of the first portion andthe second portion, and the current detection module is configured togenerate the digital value indicative of the first portion bysubtracting the first digital value from the second digital value. 4.The detection system according to claim 1, wherein, in the second mode,the mode switch is configured to enable charge accumulation on one ormore capacitive elements of the sensor for a duration of a first timeinterval followed by discharge of the one or more capacitive elements ofthe sensor to the current detection module for a duration of a secondtime interval thereby providing a pulsed current signal to the currentdetection module.
 5. The detection system according to claim 4, whereinthe one or more capacitive elements of the sensor accumulate charge fora duration of a first time interval followed by discharge of the one ormore capacitive elements of the sensor to the current detection modulefor a duration of a second time interval thereby providing a pulsedcurrent signal to the current detection module.
 6. The detection systemaccording to claim 1, wherein, in the third mode, the mode switch isconfigured to maintain charge on a capacitor of the sensor at areference value for a duration of a first time interval followed by asecond time interval during which the mode switch is configured torelease maintaining of the charge on a capacitor at the reference valuewhile enabling the capacitor of the sensor to discharge to the currentdetection module thereby providing a pulsed current signal to thecurrent detection module.
 7. The detection system according to claim 1,wherein the sensor comprises one of a photosensor, a capacitance sensor,an impedance sensor, a magnetic field sensor, or a piezoelectric film.8. The detection system according to claim 1, wherein the contributionto the current signal from the target source comprises a pulse or aseries of repeating pulses synchronized to the current detection module.9. The detection system according to claim 1, wherein the currentdetection module comprises: a first stage comprising a trans-impedanceamplifier configured to amplify the current signal and generate a lownoise signal; a second stage comprising a high pass filter configured toconvert the low noise signal into an alternating current (AC) signalhaving a positive amplitude, a negative amplitude, and a zero cross-overpoint between the positive amplitude and the negative amplitude; a thirdstage comprising: a positive integrating amplifier configured to receivethe positive amplitude of the AC signal and generate a positiveintegrated value over an integration period; and a negative integratingamplifier configured to receive the negative amplitude of the AC signaland generate a negative integrated value over the integration period;and a fourth stage comprising at least an analog-to-digital converter(ADC) configured to receive the positive and negative integrated valuesand generate the digital value indicative of the first portion of thecurrent signal and/or the digital value indicative of the second portionof the current signal based on the positive and negative integratedvalues.
 10. The detection system according to claim 9, wherein thetrans-impedance amplifier includes an operational amplifier with afeedback loop comprising a feedback capacitor and a feedback resistorand a low pass filter.
 11. The detection system according to claim 9,wherein the second stage includes an AC source and a capacitor thatprovides AC coupling.
 12. The detection system according to claim 9,wherein the third stage includes a switch configured to change from thepositive integrating amplifier to the negative integrating amplifier atthe occurrence of the zero cross-over point.
 13. The detection systemaccording to claim 12, wherein the switching action of the switch isconfigured by a timer.
 14. The detection system according to claim 13,wherein the timer is configured to provide a clock synchronized with afrequency of the target source.
 15. The detection system according toclaim 9, wherein the second stage is bypassed in the second mode and/orthe third mode.
 16. The detection system according to claim 9, whereinthe target source is a synchronous light source.
 17. The detectionsystem according to claim 16, wherein a pulse of the synchronized lightsource has a duration of τ, a bandwidth of the second stage isapproximately 1/τ, and a corner frequency of the high pass filter is setas 0.5/τ.
 18. A detection system comprising: first means for generatinga current signal, the current signal comprising at least a first portioncomprising a contribution from a target source and/or a second portioncomprising a contribution from one or more sources other than the targetsource, and generating a digital value indicative of the first portionof the current signal and/or a digital value indicative of the secondportion of the current signal; and second means for setting the firstmeans to operate in one of a first mode, a second mode, and a thirdmode, wherein: in the first mode, the first means is configured togenerate the digital value indicative of the first portion, in thesecond mode, the first means is configured to generate the digital valueindicative of at least the second portion when the contribution from theone or more sources other than the target source is in a first range ofvalues, and in the third mode, the first means is configured to generatethe digital value indicative of at least the second portion when thecontribution from the one or more sources other than the target sourceis in a second range of values, the second range of values having anupper end higher than an upper end of the first range of values.
 19. Thedetection system according to claim 18, wherein the second means and thetarget source are synchronized so that the second means is configured toset the first means module to operate in the first mode when the targetsource is generating the contribution to the current signal, andconfigured to set the first means to operate in the second mode or inthe third mode when the target source is not generating the contributionto the current signal.
 20. A detection system comprising: a sensorconfigured to generate a current signal indicative of the sensordetecting a stimuli that comprises a pulse or a series of repeatingpulses generated by a target source; a current detection module having apredetermined phase relationship between operation of the currentdetection module and the pulse or the series of repeating pulsesgenerated by the target source, and configured to determine acontribution to the current signal due to the detected stimuli from thetarget source.
 21. The detection system according to claim 20, whereinthe current detection module comprises: a first stage comprising atrans-impedance amplifier configured to amplify the current signal andgenerate a low noise signal; a second stage comprising a high passfilter configured to convert the low noise signal into an alternatingcurrent (AC) signal having a positive amplitude, a negative amplitude,and a zero cross-over point between the positive amplitude and thenegative amplitude; a third stage comprising: a positive integratingamplifier configured to receive the positive amplitude of the AC signaland generate a positive integrated value over an integration period; anda negative integrating amplifier configured to receive the negativeamplitude of the AC signal and generate a negative integrated value overthe integration period; and a fourth stage comprising at least ananalog-to-digital converter (ADC) configured to receive the positive andnegative integrated values and determine the contribution to the currentsignal due to the detected stimuli based on the positive and negativeintegrated values.
 22. The detection system according to claim 20,wherein the current signal further comprises a contribution due to thesensor detecting a stimuli from one or more sources other than thetarget source, and the detection system further comprises a mode switchconfigured to control the current detection module to operate in a firstmode or a second mode, wherein the current detection module isconfigured to determine the contribution to the current signal due tothe detected stimuli from the target source when the current detectionmodule operates in the first mode, and the current detection module isconfigured to determine the contribution to the current signal due tothe detected stimuli from one or more sources other than the targetsource when the current detection module operates in the second mode.23. The detection system according to claim 22, wherein the mode switchis configured to control the current detection module to operate in oneof the first mode, the second mode, or a third mode, and wherein thecurrent detection module is configured to operate in the second modewhen the contribution from the one or more sources other than the targetsource is in a first range of values, and the current detection moduleis configured to operate in the third mode when the contribution fromthe one or more sources other than the target source is in a secondrange of values, the second range of values having an upper end higherthan an upper end of the first range of values, to determine thecontribution to the current signal due to the detected stimuli from oneor more sources other than the target source.
 24. The detection systemaccording to claim 22, wherein the mode switch is configured to controlthe current detection module to operate in one of the first mode, thesecond mode, or a third mode, and wherein, in the third mode, thecurrent detection module is configured to: operate in the second modefor a first period of time during which the sensor is not detecting thestimuli from the target source to determine the contribution to thecurrent signal due to the detected stimuli from one or more sourcesother than the target source in absence of the contribution to thecurrent signal due to the detected stimuli from the target source,operate in the second mode for a second period of time during which thesensor is detecting the stimuli from the target source to determine acombined contribution due to the sensor detecting both the stimuli fromthe target source and the stimuli from one or more sources other thanthe target source, and determine the contribution to the current signaldue to the stimuli from the target source by subtracting thecontribution determined for the first period of time from the combinedcontribution determined for the second period of time.
 25. The detectionsystem according to claim 20, wherein: the current signal is a firstcurrent signal, further comprising a contribution due to the sensordetecting a stimuli from one or more sources other than the targetsource, the sensor is configured to generate the first current signalfor a first time period during which the sensor is detecting both thestimuli from the target source and the stimuli from one or more sourcesother than the target source, the sensor is further configured togenerate a second current signal for a second time period during whichthe sensor is detecting the stimuli from one or more sources other thanthe target source and not detecting the stimuli from the target source,the current detection module is configured to determine the contributionto the current signal due to the stimuli from the target source based ona difference between the first current signal and the second currentsignal.
 26. The detection system according to claim 20, wherein: thepulse generated by the target source or each pulse of the series ofrepeating pulses generated by the target source has a duration of τ, thecurrent detection module comprises a trans-impedance amplifierconfigured to amplify the current signal and generate a low noise signaland a high pass filter configured to convert the low noise signal intoan alternating current (AC) signal having a positive amplitude, anegative amplitude, and a zero cross-over point between the positiveamplitude and the negative amplitude, and the predetermined phaserelationship between operation of the current detection module and thepulse or the series of repeating pulses generated by the target sourcecomprisea the bandwidth of the high pass filter being 1/τ, and a cornerfrequency of the high pass filter being 0.5/τ.
 27. The detection systemaccording to claim 23, wherein: the current detection module comprises aclock, and the current detection module having the predetermined phaserelationship with the pulse or the series of repeating pulses generatedby the target source comprises one or more frequencies present in thepulse or the series of repeating pulses generated by the target beingsynchronized to the clock.
 28. A method for determining the presence ofan object using a pulsed electromagnetic field source, the stepscomprising: producing a pulse train from a first electromagnetic fieldsource; receiving at a first sensor, the pulse train having apredetermined clock phase; receiving at the first sensor, a backgroundelectromagnetic field; producing a combined signal which includes apulse train signal based at least on the received pulse train and abackground signal at least based on the received backgroundelectromagnetic field; extracting the pulse train signal from thebackground signal at least based on subtraction and the predeterminedclock phase; and, analyzing the object at least based on the extractedpulse train signal.
 29. The method of claim 28, wherein theelectromagnetic field is a quasi-static electric field.
 30. The methodof claim 29, wherein the first sensor is a first capacitive sensor. 31.The method of claim 28, wherein the first electromagnetic field sourceis a first light source.
 32. The method of claim 31, wherein the firstsensor is photodiode.
 33. The method of claim 28, further comprising thestep of producing a clock signal at least based on the predeterminedclock phase.
 34. The method of claim 33, further comprising the step ofsynchronizing the received pulse train signal with the produced clocksignal.
 35. The method of claim 28, further comprising switching betweena first mode associated with the pulse train signal and a second modeassociated with the background signal.
 36. The method of claim 28,further comprising low-pass filtering at least one of the background andpulse train signals.
 37. The method of claim 28, further comprisingdigitally sampling at least one of the background and pulse trainsignals.
 38. A system for analyzing the presence of a proximal objectusing a pulsed electromagnetic field source comprising: a firstelectromagnetic field source producing a pulse train, the pulse trainhaving a predetermined clock phase; a first sensor which senses thepulse train and a background electromagnetic field; an analog circuitwhich produces a combined signal, the combined signal comprises a pulsetrain signal based at least on the received pulse train and a backgroundsignal at least based on the received background electromagnetic field;a clock having the predetermined clock phase; a module which extractsthe pulse train signal from the background signal at least based onsubtraction and the predetermined clock phase; and, a comparator circuitwhich analyzes the object at least based on the extracted pulse trainsignal.
 39. The system of claim 38, wherein the electromagnetic field isa quasi-static electric field.
 40. The system of claim 39, wherein thefirst sensor is a first capacitive sensor.
 41. The system of claim 38,wherein the first electromagnetic field source is a first light source.42. The system of claim 41, wherein the first sensor is photodiode. 43.The system of claim 38, further comprising an analog to digitalconverter (ADC).
 44. The system of claim 43, further comprising a modulefor which synchronizes the received pulse train signal with a producedclock signal based on the clock.
 45. The system of claim 38, furthercomprising a mode switch configured switch between a first modeassociated with the pulse train signal and a second mode associated withthe background signal.
 46. The system of claim 38, further comprising alow-pass filter configured to filter at least one of the background andpulse train signals.
 47. An apparatus for determining the presence of anobject using a pulsed electromagnetic field source comprising: means forproducing a pulse train from a first electromagnetic field source; meansfor receiving at a first sensor, the pulse train having a predeterminedclock phase; means for receiving at the first sensor, a backgroundelectromagnetic field; means for producing a combined signal whichincludes a pulse train signal based at least on the received pulse trainand a background signal at least based on the received backgroundelectromagnetic field; means for extracting the pulse train signal fromthe background signal at least based on subtraction and thepredetermined clock phase; and, means for analyzing the object at leastbased on the extracted pulse train signal.